We are experiencing an issue where SRTP successfully negotiates with the carrier's media server, but the UDP Checksum field sent from the TA900 is empty. This is causing the carrier to reject the SRTP audio from the device. As I understand it, the crypto-suite AES_CM_128_HMAC_SHA1_80 ought to place a checksum in the outgoing SRTP packets, but it does not seem to be doing so. I do see a UDP checksum on the SIP signaling packets, but it is not present on the SRTP packets. The relevant configuration is below:
srtp-profile SRTP
crypto-suite AES_CM_128_HMAC_SHA1_80
voice trunk T05 type sip
description "SRTP test trunk"
sip-server primary [redacted]
srtp tls-optional SRTP
domain "[redacted]"
dial-string source to
register [redacted] auth-name [redacted] password [redacted]
grammar request-uri host domain
grammar from host domain
grammar p-asserted-identity host domain
grammar to host domain
